1. Field of the Invention
This invention relates to computerized tomography (CT) for obtaining sectional images of an examinee by emitting X-rays from radial directions to the examinee, and particularly to a method and apparatus for obtaining a plurality of sectional images of an examinee lying still.
2. Description of the Related Art
This type of CT apparatus includes an X-ray emitter and an X-ray detector opposed to each other across an examinee lying still on a top board. X-rays are emitted from radial directions to scan the examinee and collect projection data relating to X-ray absorption in the examinee's body. The data is reversely projected to reconstruct a distribution image of X-ray absorption coefficients in a sectional plane across the examinee's body, thereby to obtain a sectional image of the body. After one slice is scanned, the top board is slid to adjust a next slice of concern of the examinee to a direction of X-ray emission from the X-ray emitter, and a sectional image of this slice is obtained as above.
If a sectional plane has an excessive slice thickness, a virtual image called a partial volume artifact tends to appear in a reconstructed image of, for example, the osseous basal region of brains. In practice, as disclosed in Japanese Patent Publication (Unexamined) No. 61-109551, data of numerous thin slice planes are collected and put to data processing such as addition to obtain a clear image of a thick sectional plane.
However, such a method of obtaining a sectional image has the following disadvantage.
The top board on which an examinee lies is slid at a relatively low speed (about 2 seconds) in order to avoid a displacement between a sectional plane of a site of concern and the X-ray emitter or the like. 0n the other hand, scanning by the X-ray emitter or the like is carried out at high speed (about 1 second). To collect data of numerous sectional planes under such conditions, sliding of the top board supporting the examinee and scanning by the X-ray emitter or the like must alternately be repeated numerous times. A long time is required to collect data of all of desired sectional planes particularly because of the slow sliding movement of the top board.